(1) Field of the Invention
The present invention relates to a cassette type magnetic bubble memory device which is dismountably attached to a main apparatus comprising a bubble driving circuit and a bubble reading circuit.
(2) Description of the Prior Art
An apparatus utilizing a magnetic bubble memory device for storage of information and performance of logical operation has various advantageous characteristics, such as having a non-volatile memory, a high memory density, a small power consumption, a small size and being light weight. Moreover, since the magnetic bubble memory device is a solid device, which does not include any mechanical element and thus has a very high reliability, great expectations are held for future utilization of this magnetic bubble memory device as a console unit memory or the like. When the magnetic bubble memory device is used as a console unit memory, for example, a memory medium of a portable data recorder, the characteristics of small size and light weight are especially important among the above-mentioned characteristics of the magnetic bubble memory device. Under such background, there has recently been proposed a method in which a magnetic bubble memory device is contained in a cassette separately from a main apparatus comprising a driving circuit and a reading circuit and the cassette type magnetic bubble memory device is dismountably attached to the main apparatus. When this method is adopted, since information can be conveyed very simply and since relatively large quantities of information can be contained in a compact cassette by virtue of the characteristic properties of the magnetic bubble memory device, information to be put into a central processing unit can be formed directly at a place where data occur and therefore, further increase of the processing efficiency can be expected.
In the conventional cassette type magnetic bubble memory device, the writing and reading operations of the bubble memory device are performed only on the soft portion of a program prepared for operation of the magnetic bubble memory device. In the case where the writing and reading operations are performed only on the soft portion of the program, it sometimes happens that an operation of a different subroutine is performed because of an error of the subroutine on the program or an error of the program operation, and in this case, information stored in the magnetic bubble memory device is destroyed. Furthermore, pulse signals produced by noises or the like are introduced into the writing circuit and different information bubbles are produced in the bubble memory device.
Since the conventional cassette type magnetic bubble memory device can easily be dismounted from the main apparatus, it sometimes happens that during the operation of the device, that is, while a revolving magnetic field is being produced, the cassette type magnetic bubble memory device is taken out from the main apparatus by mistake or accident, with the result that information stored in the memory device is destroyed or contents of information is changed during the reading or writing operation of the main apparatus to reduce the reliability of the device.
Furthermore, since the cassette type magnetic bubble memory device is light and is easy to carry and handle, the cassette is frequently attached and dismounted and it often happens that the cassette is inserted conversely to the main apparatus. In order to prevent this converse insertion of the cassette, the connector-joining face of the cassette is formed to have a trapezoidal shape so that converse insertion is not allowed because of the difference of the shape between the left and right sides of the cassette. Even in this case, if the cassette is conversely inserted by a strong force, a gate pin of the joining face of the connector of the cassette is caused to fall in contact with the connector-joining face of the main apparatus, whereby the bubble memory device is readily destroyed. Accordingly, erroneous contact cannot be substantially avoided if only the joining face has a trapezoidal shape.
As pointed out before, the cassette type magnetic bubble memory device is light and is easy to carry and handle. This means that the frequency of unexpected encounters with a disturbance magnetic field is increased. For example, there is a fear of attachment of a small permanent magnet to the cassette. Since the magnetic bubble memory device has a magnetic memory element, if it is exposed to a disturbance magnetic field, there is a risk of destroying the information stored in the cassette type magnetic bubble memory device. Accordingly, a magnetic bubble chip is protected by a shield so that even if a disturbance magnetic field of about 50 to about 100 Oe is uniformly applied, the information stored in the interior of the magnetic bubble memory device is not destroyed. However, a small magnet or the like produces a local magnetic field of about 300 to about 400 Oe. Accordingly, in the cassette type magnetic bubble memory device, for which various application modes are considered, appropriate countermeasures to cope with the foregoing disadvantages should be taken.